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also observed when considering the
226
Ra in water and sediments, showing an increase in its
content. In the cases of industries located close to the seashore, tidal activity also influenced
the
226
Ra content in water. Samples collected in low tide had higher content than those in high
tide (Periáñez et al., 1993). Up to 35% of the total activity in water of
238
U and 20-30 % for
232
Th were associated with the particulate matter suspended in water filtered through 0.45 μm
pore size (Martínez-Aguirre et al., 1994). The
210
Pb also showed a tenfold increase in the
dissolved fraction, although it decreased quickly downstreams (Martínez-Aguirre et al.,
1997). In the case of the use of the HCl wet method, the
226
Ra content in contaminated banks
was within the range 2300-5400 Bq·kg
-1
; whereas its content in unaffected ones was about 13
Bq·kg
-1
(Paridaens et al., 2001).
After the banning of the direct discharges (OSPAR, 1996), modifications were introduced
in the industries and improved treatment of effluents were considered, for example close
water systems were used to transport the phosphogypsum to the stacks (Betti et al., 2004;
Bolívar et al., 2009). The banning had also impact on the naturally occurring radionuclides in
water and sediments. A self-cleaning process was reported in Spain and North West England
(Villa et al., 2009). In the Spanish case, during the period 1999-2002, the
226
Ra content in
water showed a continuous decrease from (66 ± 3) mBq·L
-1
in 1998 to (4±2) mBq·L
-1
in 2002
(Absi et al., 2004). The
226
Ra content in sediments also showed a decrease trend and a
homogenization process due to the transportation and mixing of sediments as consequence of
currents and tides (Absi et al., 2004; Villa et al., 2009). The sediment content of
226
Ra
decreased from 700 to 60 Bq kg
-1
, and that of
210
Pb from 370 to 100 Bq·kg
-1
(Villa et al.,
2009). The effective decreasing half-time was within the range 0.16-0.84 yr in water and
5.03-5.99 yr in sediments for
226
Ra, while for
210
Pb was within the range 2.38-14.94 yr (Villa
et al., 2009).
A
GRICULTURAL
U
SE OF
F
ERTILIZERS
Radiological Hazard Due to Use of Fertilizers
The fertilizers, especially the phosphate based ones, present high contents of naturally
occurring radionuclides (see Table 4). The application of fertilizers to soil increased the
content of those radionuclides. The use of several phosphate fertilizers ranging 5-50% P in
the form of P
2
O
5
in rates 7.4-12.4 kg·m
-2
for long periods of time increased the
226
Ra,
40
K,
and
232
Th content in soils from 12-26, 222-376, and 39-72 Bq·kg
-1
respectively to 33-100,
227-503, and 51-116 Bq·kg
-1
respectively (Ioannides et al., 1997). The dose due to external
exposure as a consequence of fertilizer application can be considered as negligible, about
37.4-125.8 μSv·yr
-1
(Santawamaitre et al., 2010), much lower than the 1 mSv·yr
-1
for the
general population. However, radionuclides along with nutrients do not remain immobile in
soil. They can be leached by run-off water into surface and groundwater resources, being this
one of the causes of eutrophication of water bodies (Badruzzaman et al., 2012). Other
chemical species, such as phosphates, nitrates and sulphates, also showed increased levels in
water bodies contaminated by use of fertilizers (Zielinski et al., 1997; Baeza et al., 2011;
Kamel, 2012). Uranium occurs usually in water bodies contaminated by fertilizers, and the
ratio
234
U/
238
U has been considered as a potential marker for tracking nutrient sources
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